The invention relates generally to the field of turbomachinery and, more specifically to an improved turbomachine and to a method for operating a turbomachine.
In conventional engines, approximately one third of the total heat energy of the fuel is lost in the cooling water and one third is lost in the exhaust gases. In the case of an uncooled engine, the energy yield can only be slightly increased from, for example, 34% to a maximum of 38.5%, but only by accepting an increase in the exhaust gas loss.
It is known in the art to provide, for example, turbochargers for the partial recovery of exhaust gas energy. By means of turbochargers, however, only the volumetric efficiency can, in the end, be increased in the case of piston engines, but the exhaust gas energy cannot be completely utilized.
CH 464 606 shows a method for cooling a screw-type engine, in which fresh air is heated between a compressor and a combustion chamber by means of exhaust gases in the counterflow method. In this case, the compressor is necessary for generating a pressure in order to deliver the fresh air through a eat exchanger.
DE 94 01 804 U1 and DD 276 512 A1 show internal combustion engines with two parallel screw spindles, which mesh with one another and by means of which fresh air is conveyed to a combustion chamber and combustion gases are subsequently supplied to an expansion stage.
An object of the invention is, therefore, to develop a method and a turbomachine for carrying out the method, by which the heat loss can be reduced.
With respect to the method, this object is achieved, according to the invention, by fresh air being induced as the working medium, then isochorically heated while being continuously conveyed in a delivery direction in individually enclosed delivery and heating chambers which follow one another in the delivery direction. The isochorically heated air is then introduced into a working machine, in which the excess air pressure generated by the isochoric heating is substantially removed by power output. The air is mixed with fuel before its introduction into the working machine and/or the air emerging from the working machine is mixed with fuel and combustion is initiated, the combustion gases are further heated by the combustion being guided in counterflow, i.e. against the delivery direction of the conveying and heating chambers, past the latter in such a way that the induced fresh air is successively and isochorically heated during its continual conveyance in the delivery direction in the conveying and heating chambers.
The object mentioned above is achieved, with respect to the appliance or turbocharger aspect of the invention, by means of at least two meshed axially parallel screw spindles which can be driven in opposite directions but with the same rotational speed. These screw spindles are each configured as a hollow shaft, which form-together with an externally insulated stator tightly enclosing it on the casing side-substantially enclosed respective air chambers extending over a threaded section. During rotation of the screw spindles the chambers are displaced in the axial delivery direction from an air induction connection to an air inlet region of a working machine torsionally connected to the screw spindles. A combustion chamber is provided before the air inlet of the working machine and/or after the air outlet of the working machine. The combustion chamber has a fuel supply and ignition device. The exhaust gases are respectively introduced via an exhaust pipe into an end of a shaft hollow space opposite the air induction connection, which shaft hollow space is configured relative to the air chambers as a counterflow heat exchanger and opens into an exhaust in the region of the air induction connection.
According to the invention, therefore, a part of the heat energy generated by the combustion is converted back into pressure, which results from the isochoric heating of the working medium enclosed in the air chambers. The air pressure gained in this way then performs work in the working machine which can, for example, operate in an opposite sense to the screw-type compressor and the shaft rotation generated by this can be partially utilized, in a preferred embodiment, for air pre-compression at the beginning of the shaft, for example in a screw-type compressor.
After the expansion in the working machine, the air pressure in the heat exchanger drops to the extent necessary to overcome the flow resistances. On the other hand, the air temperature does not fall so rapidly, in accordance with the thermodynamic laws for polytropic expansion, so that the further heating of the air in the afterburner can start from a temperature level which is already high. It is therefore possible to operate with a temperature difference of, for example, some 50xc2x0 C.-100xc2x0 C. in the counterflow heat exchanger.
In the system according to the invention, only slight heat losses occur in the insulation covering the system toward the outside; the exhaust gas losses can also be kept very low. Although the system according to the invention requires heat-resistant materials, these are not so severely loaded as, for example, blades/vanes in jet turbines. The system according to the invention is therefore particularly suitable for efficient electricity generators, automobile engines, marine engines and the like.
With respect to the method, it is expedient for the temperature of the combustion gases to be reduced along the counterflow heat exchanger section to approximately the temperature of the induced fresh air and, by this means, for the efficiency to be further increased.
The power can be further increased somewhat by at least part of the fuel being introduced into the isochorically heated trash air before the working machine and by at least partial combustion having been already initiated before the working machine. It is also possible to provide for water to be induced or injected into at least some of the delivery and heating chambers.
The working machine can be a turbine, which can operate on the same shaft as a compressor connected upstream of each screw spindle. Instead of a compressor connected upstream, or in addition to it, compression of the induced fresh air can then take place by each screw spindle having at least one axial section with a thread pitch which decreases in the conveying direction.
In contrast to CH 464 606, fresh air is, according to an aspect of the invention, conveyed in separate conveying and heating chambers in which heating takes place. Because of this, it is not necessary to use a compressor for generating a pressure drop; however, a compressor can be connected upstream in order to deliver compressed fresh air.
In contrast to DE 94 01 804 U1 and DD 276 512 A1, the shaft hollow space is, according to the invention, used as a counterflow heat exchanger for the air chambers so that the isochoric heating, according to an aspect of the invention, of the individual, substantially enclosed air chambers, which are conveyed in the axial direction to the working machine, is made possible.
Further features of the invention are explained in more detail in association with further advantages of the invention, using an exemplary embodiment.